Gas-cooled, in particular air-cooled, generators in the power class of a few 100 MVA with a rotating exciter have long been offered by the applicant. Those details of these known generators which are critical for cooling are reproduced in FIGS. 1 to 3. The generator 10 of FIG. 1 is built on a stable box-shaped base frame 11 which is delimited laterally by continuous U-profiles and has bollards 54 which project laterally on the longitudinal sides and at which the generator 10 can be lifted by means of a crane or the like. The base frame 11 has fastened on it by means of a plurality of carrying rings 13 a hollow-cylindrical stator 12, the cylindrical inner space 17 of which receives a rotor, not illustrated, which is indicated in FIG. 1 by a generator shaft 35 carrying the rotor. The rotatable mounting of the rotor or generator shaft takes place by means of bearing blocks (34 in FIG. 5) which are fastened on the top side of the base frame 11 on carrying plates 18, 19 provided specifically for this purpose. In the assembled state, the stator 12 is surrounded by cooling-air chambers which are constructed from individual wall elements 22 (FIG. 1 shows only the lower part of the chambers divisible along a horizontal parting plane). The cooling-air chambers are connected partially to one another by means of connecting ducts running within the base frame 11 and partially to coolers arranged above the stator 12, thus giving rise to a cooling circuit which runs through the rotor and stator and the associated windings and air gaps and which includes the base frame 11 as part of the circuit.
According to FIGS. 2 and 3, that region of the base frame 11 which is assigned to the stator 12 is separated from the region following in the axial direction and assigned to a rotating exciter 24 by means of a transverse wall 25 which merges at each of the two ends into a bollard 54. In the exciter region of the base frame 11, two parallel intermediate walls 55 and 56 running in the axial direction separate two lateral cavities 20 and 21, between which is located a third, larger cavity which is itself subdivided in the middle by means of a transversely running intermediate wall 57 (see also FIG. 4, 5). The outer part of the middle, larger cavity is connected to the lateral cavities 20, 21 by means of (circular) perforations 16 in the intermediate walls 55, 56. The lateral cavities 20, 21 are connected to the stator region of the base frame 11 via corresponding perforations in the transverse wall 25. The middle, larger cavity is closed off at the top by means of a cover plate 14 which has two rectangular ports 15, 15′ lying next to one another. Each of the two ports 15, 15′ allows access into an underneath part region of the middle cavity.
As may be gathered from FIG. 3, above the port 15′ the rotating exciter 24 is arranged, which discharges the cooling air flowing through it through the port 15′ downward into the underneath cavity, from where it flows back to that region of the base frame 11 which lies below the stator 12. The exciter 24 receives the cooling air via an air supply hood 23 (FIG. 3) which is arranged above the port 15. According to the flow arrows depicted in the base frame 11 in FIGS. 2 and 3, cooling air passes out of the stator region of the base frame 11 through the perforations in the transverse wall 25 into the two lateral cavities 20, 21, from there through the perforations 16 in the intermediate walls 55, 56 into the outer part of the middle cavity, and from there through the port 15 upward into the air supply hood 23. The air supply hood 23 then ensures that the cooling air is fed axially into the exciter 24.
This type of routing of cooling air within the base frame 11 has the disadvantage that, because of the constantly changing diameters in the flow path, considerable pressure losses occur which impair the cooling-air stream and consequently the cooling efficiency.